Considerable publicity has already emerged on the new S stock trains being delivered to the Metropolitan Line.

However, these are only part of a massive overall programme to upgrade all of London Underground’s sub surface lines. With a variety of ageing rolling stock, and some signalling systems that date back to the 1940s, the lines are overdue for modernisation.

Hedley Calderbank is the Upgrade Sponsor within London Underground (LU) to ensure that the project plans are financially on course to deliver all the required benefits to LU’s business.

He gave the rail engineer a fascinating insight into the project, its planning and delivery.

The business plan

In the PPP era, the two organisations awarded the contracts were required to put forward plans for major improvement works. Metronet, responsible for the Sub Surface Railway (SSR), was committed to a complete upgrade of trains and signalling on all those routes as a single project.

The existing track layouts had been unchanged for years – some even dated back to the loco hauled days of the Metropolitan Railway. Piecemeal renewals had kept everything largely unchanged as this had been the simplest thing to do.

As a result, many track layouts were less than optimised for the existing train service while the capabilities of both signalling and rolling stock fell well short of LU’s aspirations for capturing more traffic.

The PPP organisational structure has been overtaken by events, but it was the catalyst for developing the SSR scheme as a single entity embracing the Metropolitan, District, Circle and Hammersmith & City lines.

The ensuing business case for the upgrade has been based around a number of elements:

  • Shorter journey times for passengers – entry gate to exit gate
  • Faster trains with better acceleration
  • Provision of more frequent trains, thus giving less waiting time on station platforms
  • Higher speeds on the Metropolitan line out in the north-west suburbs
  • Fulfilment of suppressed demand because of existing service limitations

Considerable work has gone into proving that the business case is robust. The peak number of trains per hour on every route will be increased as follows:

  • Metropolitan Line – from 21 to 28
  • Circle and Hammersmith & City (central section) – from 28 to 32
  • District (central section) – from 28 to 32
  • Hammersmith & City – from 7 to 16, already partially achieved by the extended Circle line
  • District Line branches – by 1 train on each

Many of these additions are interdependent but, once the existing signalling has been replaced, the peak passenger capacity of the network will be increased by more than 30%.

Layout constrictions and improvements

The SSR group of lines has four major junctions where little can be done to eliminate flat crossings: Aldgate, Baker Street, Edgware Road and Earls Court.

To provide grade-separated layouts would be prohibitively expensive. However, running more trains across the conflicting paths can be simplified by changes to the track layouts, the signalling system and the use of ATR (Automatic Train Regulation).

One example is the Metropolitan line at Baker Street which has two through platforms and two terminating bays. The new service envisages 28 trains per hour with 12 terminating and 16 running onto the Circle line.

This can be achieved by minor adjustments to the track layouts and by changing the signalling to give better ‘run in’ times to platforms so that over restrictive overlaps are removed.

Elsewhere, there are around 30 locations where even minor changes to the layout can give improved operating flexibility and/or higher speeds, as well as providing the opportunity to terminate trains at additional stations.

Some of those locations will have new trackwork with fewer point ends and thus cheaper signalling and less maintenance. Bi-directional signalling enhances these simplifications at some sites.


Installing a Bailey Bridge at Neasden for construction traffic access. Photo: the rail engineer.

The Signalling Work and Contract

As important as the provision of the new trains is the resignalling of the entire SSR network with a modern Automatic Train Control (ATC) system.

The signalling work contract has recently been let to Bombardier for a value of around £350m based upon their CITYFLO 650 product which has been proven on the Metro de Madrid and the Shenzhen Metro.

The terms and conditions for implementation are predictably quite onerous. For the first time on LU, there will be no major blockades permitted for signalling installation, testing or commissioning, although some closures will, of course, be needed for trackwork changes.

The ATC system will first be tested and proven by Bombardier on the Old Dalby test track in the East Midlands. This is planned for 2012/3. Thereafter the new lineside signalling equipment will be progressively installed with the intention of testing it in traffic while in shadow mode.

It will be switched to be live during engineering hours to enable testing to be carried out, but switched back to the old system ready for traffic the next day. The system will have all the features one would expect of a modern metro:

  • Automatic Train Protection – continuous with elimination of train stops
  • Moving Block, allowing variable headways
  • Attended Automatic Train Operation retaining the driver in leading cab
  • In-cab display showing movement authority status and no lineside signals
  • Automatic Train Regulation with junction optimisation

Lineside equipment is much reduced with most of the active equipment on board the train. Space was designed into the rolling stock design for the new signalling equipment.

However, as some new trains have already been delivered, these will need to be retro-fitted as will the engineering fleet. Later builds of the trains will have the in-cab signalling fitted as original equipment at the Derby factory.

The new Service Control Centre has already been built. A second disaster recovery centre will also be provided in due course. All communication to and from trains will be by radio which will use conventional aerials on the overground sections.

However, radiating cable will be needed at some locations in tunnels where antenna mounting is not possible. It is intended that a dual transmission path will exist continuously to all trains, resulting in an extremely robust communication system.

To achieve this, both cab units on the train will be active and will receive radio data by independent paths. The cab units will be connected together via an on-train fibre link.

A new fibre network will be installed to convey safety critical instructions to the trackside transmitting points.

Train position will be confirmed by small track-mounted balises. Axle counters will be used for secondary detection only. They will not be needed under normal operation but, should disruption occur, then they will be part of the recovery process.

Point machines of varying types – pneumatic and electrical – will remain where the layout is unaltered, but for new trackwork LU will standardise on a modern in-bearer clamplock design on ballasted track and the Surelock point mechanism elsewhere.

Since station dwell times will be critical in achieving service performance, the driver will have responsibility for door closing, aided by an in-cab countdown clock.


Track relaying. Photo: the rail engineer.

Interfaces with other lines

The Metropolitan and District lines share tracks with the Piccadilly line from Rayners Lane to Uxbridge and Barons Court to Acton.

The District line operates over Network Rail tracks to Wimbledon and Richmond while the Metropolitan line has to accommodate Chiltern Railways trains over its tracks from Harrow to Amersham.

Different philosophies are being employed to cater for the continued safe operation of these “alien” train services.

On the Piccadilly line sections, studies have shown that it is more cost effective to equip the trains with the new SSR ATC equipment rather than to provide dual ATC and lineside signals.

This will also allow interoperability of tracks between Barons Court and Acton so permitting both District and Piccadilly trains to run on either track.

The full ATC system will be provided on the Wimbledon branch from Putney Bridge to Wimbledon in addition to the legacy lineside signalling for the few non-LU trains.

From Gunnersbury to Richmond, the ATC system will be overlaid on the existing conventional Network Rail signalling. On the Chiltern line, there will be lineside signals in parallel with the full ATC system for Marylebone to Aylesbury trains.

Provision may need to be made at Watford for the extension of the line to Watford Junction under the Croxley Link scheme now under active consideration by Hertfordshire County Council.

Should the project come about, this will mean another interface with Network Rail signalling at Watford High Street.

The Chesham branch will remain ‘One Train Working’ but the junction will be moved northwards from Chalfont & Latimer to gain greater capacity.


New S stock train on the Metropolitan line. Photo: the rail engineer.

Project Phasing and Priorities

8-car S stock trains are already entering service on the Metropolitan line and deliveries will be complete by 2013. These will take over from the A stock that has been in service since 1960 and are LU’s oldest trains.

The new trains have, however, necessitated some adjustments to the existing signalling to cater for slightly longer cars, a different driving position and altered signal sighting.

Before the new ATC signalling can be brought into public service use, all trains on a particular route must be operated solely by the new stock.

New signalling can then be commissioned on the Uxbridge branch and then progressively on the rest of the Metropolitan line by 2016, although not at that stage from Baker Street to Aldgate.

Similarly, on the Circle, Hammersmith & City and District lines, which will all receive 7-car S stock sets, the existing signalling will be modified so that trains can be driven for a period in manual mode.

S stock deliveries will be complete in 2016 whereupon the new signalling will be commissioned on the Circle and Hammersmith & City routes, with the District line finally being converted by 2018.

The complexities of this project should not be underestimated. It will be considerably more difficult to achieve than the recent Victoria and Jubilee line upgrades as these were essentially end-to-end routes with no intermediate junctions.

There will no doubt be issues surrounding the required safety case, although a measure of cross acceptance will be applicable as the technology has successfully been applied elsewhere.

To facilitate this, LU has every intention of not deviating from the standard signalling product even if this means changing its operating rules.

It is going to be fascinating over the next seven years to watch the work as it progresses.

The end result will be a world class metro operation that should be good for an intended life of 40 years.